Did you know that mammal infants begin to suckle mom’s milk through a learned response that centres on learning her unique combination of smells?
A new study has found that when a mammal is born, it is exposed to the smell of its mother’s amniotic fluid and the baby responds to these very smells to feed.
Initially, researchers thought that pheromones, (which are chemicals that trigger innate behaviour), drove the suckling response as an automatic behaviour.
Smells must be learnt before breastfeeding
However this new finding shows that, in mice, the smells must be learnt before the behaviour can occur.
This research offers an opportunity to investigate the biology of instinct.
Earlier studies showed that European rabbit moms use a pheromone to initiate suckling in their newborns. This led most scientists to believe that all mammals were likely to use the same process.
Eager to discover the pheromone involved in other mammals, researchers chose the mouse, since they have a similar parenting style to that of humans.
“We were expecting to find a pheromone controlling suckling in mice, but we found a completely different mechanism at work,” Dr Darren Logan, lead author of the study from Wellcome Trust Sanger Institute, said.
“We have shown for the first time that it is not a pheromone response in mice, but a learned response, founded on a mix of odours: the unique signature smell of the mother,” Logan said.
To unravel the smells involved in initiating suckling, the researchers introduced newborn mice delivered by C-section to breasts that had been washed clean and then soaked in one of the fluids that a baby would first inhale at birth. Such as the mother’s saliva, amniotic fluid, breast milk and urine. Only the breasts that smelt of the mother’s amniotic fluid initiated suckling.
The team then tested for the presence of a pheromone in the amniotic fluid. They fed pregnant mice strong smelling foods, such as garlic, to change the signature odour of the mother.
No species-wide pheromone that makes mammal infants feed
According to the researchers, if a pheromone was involved, the garlic would have no effect on suckling. Results showed that only those mice that had previous exposure to the amniotic fluid with the strong smell from their mother were able to feed successfully, proving the signature odour must be learned.
“Our work shows us that there is no species-wide pheromone that makes newborn mice feed, but that the mouse pups are actually learning their mother’s unique and variable mix of smells at birth,” Lisa Stowers, senior author from The Scripps Research Institute, said.
“So, although the suckling response may look like a pheromone-mediated behaviour, it is actually initiated through a fundamentally different process,” she said.